Western corn
rootworm

WESTERN CORN ROOTWORM

Diabrotica virgifera

The western corn rootworm is one of the most important pests in maize cultivation. It belongs to the family of leaf beetles (lat. Chrysomelidae). It was introduced from America at the beginning of the 1990s and has been spreading continuously in Europe ever since. The corn rootworm is the most important maize pest in the USA, and most insecticides are applied against it worldwide. The corn rootworm is an approx. 5mm long, black-yellow coloured beetle with long antennae. The beetle flies from July to October.

LIFE CYCLE OF WESTERN CORN ROOTWORM

The eggs of the western corn rootworm overwinter in a dormant state (diapause) in the soil. The larvae develop in spring and start feeding on the maize roots after hatching. They go through 3 larval stages, pupation and hatching of the adult beetles takes place in summer. In autumn, the beetles begin to feed on corn pollen, corn silk, stigma, leaves and cobs for about 2 weeks. They then lay their eggs at a depth of approx. 30 cm,  mainly in the soil of maize fields. The corn rootworm forms one generation per year.

DAMAGES CAUSED BY WESTERN CORN ROOTWORM

The main damage is caused by the larvae of the corn rootworm, but the beetles can also cause damage.

Root feeding is caused by the larvae, which first eat root hairs and later also larger roots and bore into the roots. As a result, the plants absorb less water and nutrients, which can lead to considerable yield losses. The beetles feed on pollen, silk (stigma threads), stigma, leaves and cobs of the maize plant.

The main damage is caused by the larvae feeding on the roots. The plants can be easily pulled out of the soil. A tube system is found in the root system. Typical damage is the ‘swan neck’, corn plants that lie downwards. By feeding on the hubs, the adult beetles cause unevenly developed and thus reduced grain plants.

The beetle is a ‘maize specialist’, but can also feed on the pollen of most flowering plants. Flying beetles can also lead to yield losses in pumpkin cultivation.

CONTROL OF WESTERN CORN ROOTWORM WITH NEMATODES

Nematodes are tiny, thread-like soil organisms about 0.6 mm long. They are natural enemies of the corn rootworm. The nematodes penetrate the larvae and pupae of the corn rootworm and release bacteria. This infection leads to the death of the insect within 1-2 days.

The nematodes multiply in the larvae and leave the dead insect in their thousands to search for more living corn rootworm larvae.

This continuous reproduction and build-up of the nematode population has a lasting effect.